An amplifying circuit is usually required to have a constant gain during the whole working temperature range in some applications, such as in a hall voltage amplifying circuit. For example, when a hall sensor is used to sense a current, the bandwidth of an amplifying circuit in the hall sensor is required to be very narrow to decrease the effect of white noise which exists in the whole bandwidth. For the gain of an amplifying circuit has a relationship with its bandwidth, the gain of the amplifying circuit will vary with the temperature. Now the method of trimming is usually adopted to keep the gain constant, which is very cumbersome and complicated.
In light of above description, an amplifying circuit having a constant gain during the whole working temperature range and a simple architecture is required to solve at least one of the above problems.